It is always desirable to be able to provide a new service which can be made compatible for transmission over an existing medium, such as a cable or satellite link which is capable of propagating a predetermined bit transmission rate or signal format. One such application is disclosed in the article "Design Technique For Multiplexing Asynchronous Digital Video and Audio Signals" by J. H. Stott in IEEE Transactions on Communications, Vol COM-26, No. 5, May 1978 at pages 601-610. There, apparatus is designed for providing multiplexed asynchronous digital video and audio signals in a predetermined signal format for transmission on a 120 Mbit/s digital line system or a 60 Mbit/s Intelsat IV satellite link. In the Stott arrangement, one asynchronous video and six audio signals are multiplexed into sequential frames, where each frame comprises 300 six-bit words as shown in FIG. 5 of the article. These sequential frames form the structure of the 60 Mbit/s multiplexed signal. Since the video signals are asynchronous, "justification", also known as "pulse stuffing" techniques, are used to aid in providing the 60 Mbit/s signal format.
A lightwave system for transmitting voice and data signals is described in the article "FT3C--A Lightwave System for Metropolitan and Intercity Applications" by J. R. Stauffer in IEEE Journal On Selected Areas In Communications, Vol. SAC-1, No. 3, April 1983 at pages 413-419. The FT3C lightwave system multiplexes three 90.524 Mbit/s signals on a single-fiber pair and interfaces with DS1, DS1C, DS2 or DS3 signals. The regular FT3C line terminates in a MX3C Lightwave Terminating Frame (LTF) and the Lightwave Terminating Module in the LTF combines two DS3 signals and inserts framing, parity, pulse stuffing indicator and auxiliary bits in accordance with a signal format shown in present FIG. 1, and referred to hereinafter as the 90A format. Since the 90A signal format is sent over the FT3C line, the test equipments for use with the FT3C system are designed to operate with such signal format.
In the 90A signal format shown in present FIG. 1, the F.sub.1 F.sub.0 designations each equal a "10" bit pair which locates each 174-bit block of information, the A.sub.1 -A.sub.4 designations indicate the bit locations associated with auxiliary channels 1-4, respectively, the P.sub.1 and P.sub.2 bits comprise the two parity bit locations, and the C.sub.a to C.sub.c bit locations provide the stuffing bit indications. The 90A format of FIG. 1 is transmitted starting at the top left-hand corner of the figure and proceeds across the rows to the bottom right-hand corner of the figure.
The problem remaining in the prior art is to multiplex one video and a plurality of audio signals into a signal format which is compatible with the 90A signal format which permits both the transmission of the multiplexed signal over a FT3C line and, in turn, the adoption of the FT3C test equipments and maintenance practices.